This proposal is to acquire a high resolution gas chromatograph mass spectrometer for use by a group of eight NIH-supported biomedical research groups. A major use of the instrument would be for the measurement of prostanoids and leukotrienes in biological specimens. Additional applications would include the quantitative measurement of other biologically active ultra-trace compounds such as dopamine and 1,25-dihydroxycholecalciferol. The structural identification of two insulin mediator peptides purified from muscle tissue using fast atom bombardment mass spectrometry is proposed. Also proposed is the assessment of calcium homeostasis in the maternal/fetal system using stable calcium isotopes, with analysis by high resolution fast atom bombardment. The eight areas of research which would be aided substantially by the acquisition of the mass spectrometer are as follows: 1. Endocrine regulation of ovarian function; 2a. The role of dopamine agonists in treating prolactin secreting tumors; b. The mechanism of action of growth hormone releasing factor; 3. The relationship of sodium sensitivity and blood pressure response; 4. Assessment of vascular endothelial integrity in vitro; 5. The relationship of prostanoids and receptor-stimulated hormone release; 6. Characterization of the peptide family of mediators of insulin action; 7. The role of prostaglandins and dopamine in the hormonal control of blood pressure, fluid and electrolyte balance; 8. Calcium homeostasis for the mother and fetus.